1. Field of Invention
This invention relates generally to molding processes, molding control processes, and molded parts.
More particularly, the invention relates to a color variation and color sequencing control process for molding multi-colored plastic and composite articles, and which, while suitable for molding many multi-colored parts, is particularly useful in molding parts where a degree of controlled randomness is desired such as to simulate the natural coloring and/or marbling of slate, marble and other rocks, or the color grains of wood materials.
2. Background Art
Many processes are known for molding multi-colored plastic and composite articles. Two such processes are described briefly below, along with certain known drawbacks and disadvantages of each process.
Liquid Color Injection. This is a process where an organic color liquid is directly injected into the screw section of an injection molding press. This causes color streaking and swirling on the final product. Some of the disadvantages of this process include the following: It is not possible to consistently obtain a realistic look simulative of, for example, naturally occurring slate, because of the unnatural swirling and unnatural color transition. The organic colors do not hold up well in the sunlight, and tend to fade and discolor under extended UV exposure. It is also not possible to achieve an adequate control level for the process to allow true natural look with the above-noted desired randomness. Only one product can be run through the injection molding machine at a time, so the standard clean out and shutdown of a machine are needed to switch colors. In addition, the concentrates of the organic color liquid are high in cost, resulting in a higher cost molded product.
Color Concentrates/Streaker Pellets. With this process a concentrated color is used to streak the material to be molded. This colored material is added at the hopper and melts at different temperatures in the barrel causing streaking or blooming effects. Some of the disadvantages of this process include the following: As with the liquid color injection process, it is not possible to consistently obtain a realistic look simulative of, for example, naturally occurring slate, because of the unnatural swirling and unnatural color transition. Again, it is not possible to achieve an adequate control level to allow true natural look with the above-noted desired randomness. And again, only one product can be run at a time, so the standard clean out and shutdown of a machine are needed to switch colors. In addition, the streakers are high in cost, resulting in a higher cost molded product.
Numerous other processes are known for molding multi-colored plastic and composite articles. However, none of the prior processes eliminate the above-described drawbacks for molding parts suggestive of naturally occurring materials with random marbling or like effects.